Deposition printing, such as for example Drop on demand (DOD) inkjet printing or aerosol printing, is known in the art. Such printing may be typically used for low speed, low volume print jobs, such as, for example, large format digital printing for the signage market, and low quantity printing of textiles.
Reference is now made to FIGS. 1 and 2 which together illustrate a prior art one pass in-line printer system 100. System 100 comprises a conveyor 120 on which print media 10 is placed, static jetting arrays 140 which drop ink onto print media 10 and a jetting controller 150 which indicates to jetting arrays 140 when and how to print to produce a printed image 115 as per input image data 155.
One or more jetting arrays 140 may be used to print each color that may be used by a print job. One or more additional jetting arrays 140 may also be dedicated to the application of additional coatings or varnishes as required. As illustrated in FIG. 2, a jetting array 140 is organized into print units 160. The print units are static with respect to each other. Each print unit 160 consists of one or more print heads 170, and each print head 170 may have several dozen or even hundreds of nozzles 180, although for the sake of clarity, only a few are shown in FIG. 2. Multiple print heads 170 may be used together to speed up the print process and/or to print-images of varying degrees of resolution.
Jetting controller 150 (FIG. 1) transmits a stream of commands to jetting arrays 140 that control the jetting of nozzles 180 in order to translate image data 155 to printed image 115. As print media 10 passes underneath jetting arrays 140, jetting arrays 140 may remain in a static position and nozzles 180 can then jet onto print media 10. Each nozzle 180 may jet thousands of drops per second during the printing process.
Nozzles 180 may suffer defects that may partially or wholly impair their effectiveness. Such nozzles may stop jetting or may jet poorly. Such defects may be of either a temporary, or a permanent nature.
DOD inkjet systems and other deposition printing systems, such as aerosol jetting printing system or a dispenser, may therefore require frequent maintenance to prevent or repair such defects, and to ensure the ongoing reliability of the dispensing heads. Such maintenance may include, for example, in the case of inkjet, purging the nozzles with liquid or air, wiping and/or brushing the nozzles and/or the orifice plate, fire jetting with the entire group of nozzles or part of them, heating or cooling the nozzles, or washing the heads with liquids. Nozzles with permanent defects may be replaced.
Typically, such maintenance may be performed several times during a printing hour. Repeated stoppage of the printing process to perform maintenance may slow down the printing process and consequently raise the cost of printing. Conversely, failure to perform timely maintenance of the nozzles may result in poorer print quality and higher equipment costs as a higher percentage of nozzles may be permanently damaged and may need to be replaced.
The most common implementation of DOD inkjets for printing applications, such as graphic arts and others, entails multiple passes over the same area. The jetting heads pass over the same area a number of times, each time with a small shift so that each nozzle jets in several slightly different locations. The resulting print area for a given nozzle may therefore be overlapped by the print area for one or more other nozzles. Since the same area is printed by more than one nozzle, these overlapping print areas may serve to mitigate the effects of a defective nozzle that jets poorly or not at all. Accordingly, the use of such multiple pass jetting with overlapping print areas may enable a system to create quality prints even with several defective nozzles. It is highly desired to have a one pass jetting system capable of compensating for defective nozzles to enable creating quality prints.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.